The broad, long-term objectives of this application are to provide evidence about the potential health benefits of regular aerobic exercise in overweight children, who are therefore at increased risk for nonalcoholic fatty liver disease and atherosclerosis. The specific aims will examine the cross-sectional associations of liver injury (including liver fat, visceral fat, inflammation, and fibrosis) with risk for atherosclerosis (arterial stiffness) and other cardiovascular risk factors, and will test the effect of an after-school exercise program on these measures. This is a revision (i.e. competitive supplement) to add these measures to an ongoing project, R01 HL087923, which is testing the effect of the exercise program on cognitive outcomes. Therefore, this project may be performed sooner and at significantly lower cost as a supplement than as a separate project. PUBLIC HEALTH RELEVANCE: An unexpectedly high prevalence of nonalcoholic fatty liver disease has recently been documented in overweight children. This is a serious health condition which can lead to liver failure and cardiovascular disease, such as atherosclerosis. Weight loss can improve this condition, but little is known about the specific effects of exercise. This project will examine the links between liver health and risk for atherosclerosis in overweight and obese children, and will test the effect of a long-term after-school exercise program.